Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain
CELL METABOLISM

Note: I spent two weeks reviewing this study because it was published during midterms for one, and because I think it’s the most valuable study on diet I’ve come across in the last 3 years of reviewing scientific literature.

There’s a weight loss adage that insists calories in should be less than calories out. It’s simple math, right? This logic has never made sense to me, as quality seems important, too, if not essential.

Today’s study attempts to address that question to see if it’s the total calories consumed, or the types of calories that drives dietary weight gain. Also, are there any beneficial effects of reducing ultra-processed foods, or harmful effects of increasing them?

But first, why is a Go-gurt considered "ultra-processed"? How's this: ultra-processed means “formulations mostly of cheap industrial sources of dietary energy and nutrients plus additives, using a series of processes." In other words, a calorie is not a calorie. This stuff is far from plants and animals, which is concerning as this constitutes the majority of calories consumed in America.

The study

A group of 20 healthy, 30-somethings volunteered to residein a clinic for 28 days, ensuring everything they ate was recorded by researchers. Free food and a stationary bike? Sign me up.

The inpatient part of this research is key because a) it's rare to analyze someone’s diet continuously for a day, let alone 4 weeks, and b) it's even more unusual to assign someone two different diets, one presumably healthier than the other, and then gain valid results because you’re certain they complied.

Once in the Big Brother house, each participant was put on an unprocessed food diet for two weeks. Metrics were recorded daily, including total calories consumed, and all the blood work, from hormones to cholesterol to blood sugar. This was followed by two weeks on an ultra-processed food diet, and once again, more labs. In both cases, each participant was given 3 meals a day plus snacks, and told to eat as much as they wanted.

The ultra-processed meals included things like honey nut cheerios, blueberry muffins, Chef Boyardee ravioli (an old favorite of mine), white bread, diet lemonade, and cookies. Dinners contained vegetables covered in a suspect-looking gravy.

The unprocessed menu included Greek yogurt with fruit and nuts, spinach salad with chicken and bulgur, a beef roast with rice pilaf, steamed broccoli, and a side salad. There was no mention of wine.

In case you were wondering as I was, both diets contained meals with the same amount of total calories, energy density, macronutrients, fiber, sugars, and sodium (all the things we think might cause weight gain). That said, by not limiting how much participants could eat, researchers could observe which set of foods led to more eating. You would expect participants to eat roughly the same amount of calories regardless of the food presented.

The Results

While on the ultra-processed diet, participants ate an additional 508 calories per day and gained an average of two pounds in just two weeks. This was a stark contrast to the unprocessed diet, where they lost about two pounds in two weeks.

Researchers found that ultra-processed food encouraged overeating, likely because it lowered hormones like PYY that normally squash hunger. This type of diet also encouraged more carb and fat eating, meaning more calories.

Finally, after analyzing all the food, they noted that what made the diets so different were three main ingredients: the unprocessed meals had substantially less addedsugar and saturated fat, but also more fiber, and more omega-3 fatty acids. Basically all the things we preach.

Takeaway

The rise in obesity and type 2 diabetes occurred in parallel with our industrialized food system, but to date no one has studied an ultra-processed food diet compared to an unprocessed food diet. That is until last week. This data suggests that eliminating ultra-processed foods (white bread, cheerios, diet lemonade)  from the diet can result in weight loss, whereas a diet high in these ultra-processed foods leads to weight gain.

The results also show that the the high salt, sugar, and fat found in ultra-processed foods might not be the driver in weight gain–it’s actually much more complex, involving tampering with hormones that help control appetite. The calorie in, calorie out debate lives on.

Of note, this study also found the healthier diet was only $40 more per week, costing a reasonable $151 dollars per week compared to $106.